Lizards are reptiles of the order Squamata, which they share with the snakes. They are usually four-legged, with external ear openings and movable eyelids. Species range in adult length from a few centimeters (some Caribbean geckos) to nearly three meters (Komodo dragons).

Some lizard species called "glass snakes" or "glass lizards" have no functional legs, though there are some vestigal skeletal leg structures. They are distinguished from true snakes by the presence of eyelids and ears.

Many lizards can change color in response to their environments or in times of stress. The most familiar example is the chameleon, but more subtle color changes occur in other lizard species as well.

Lizards typically feed on insects or rodents. A few species are omnivorous and can also eat plants. Only two lizard species are poisonous: the Mexican beaded lizard and the Gila monster, both of which live in northern Mexico and southern Texas. They are typically not hazardous to humans as their poison is introduced slowly by chewing, rather than injected as with most poisonous snakes.

Other small lizards are harmless to humans (most species native to North America, for example, are incapable of drawing blood with their bites).

Most lizards lay eggs, though a few species are capable of live birth.

Lizards in the Scincomorpha family, which include skinks (such as the blue-tailed skink), often have shiny, iridescent scales that appear moist. But like all other lizards, they are dry-skinned, generally preferring to avoid water (though all lizards are able to swim if needed).